Orthopedic joint replacement surgery may involve arthroplasty of a knee, hip, or other joint (e.g., shoulder, elbow, wrist, ankle, finger, etc.). During joint replacement surgery, a surgeon typically removes diseased bone from the joint and replaces the resected bone with prosthetic implant components. Challenges of joint replacement surgery include determining the appropriate position for implant components within the joint relative to the bone and other implant components and accurately cutting and reshaping bone to precisely correspond to the planned placement of the implant components. Inaccurate positioning of implants may compromise joint performance and reduce implant life.
An important aspect of implant planning concerns variations in individual anatomy. Anatomical variation complicates implant planning because there is no single implant design or placement of implant components that provides an optimal solution for all patients. Implant planning is further complicated when the joint is subject to a disease state, such as osteoarthritis, that causes defects (e.g., osteophytes, capsular adhesions, osteochondral defects (OCD), and the like) that prevent the bones of the limb from achieving a desired alignment, such as a neutral alignment. For example, when a person with a healthy knee joint is in a standing position and the joint bears weight, the femur and tibia are neutrally aligned such that the center of the femoral head (i.e., the hip center), the center of the knee joint (i.e., the knee center), and the center of the ankle joint (i.e., the ankle center) are in line. This results in a neutral leg alignment (i.e., a neutral limb pose) in which the relative poses (i.e., position and/or orientation) of the femur and the tibia result in both the medial and lateral femoral condyles articulating with the tibial articular surface. In contrast, when a person has disease in one compartment of the knee joint (e.g., medial or lateral), the diseased compartment may collapse, causing the limb to adopt a non-neutral or misaligned pose.
One goal of implant planning is to determine a placement of implant components that will sufficiently correct the disease state such that proper or appropriate joint kinematics are restored. Appropriate joint kinematics may vary from person to person based on the unique anatomy of each individual. For example, appropriate joint kinematics may be achieved by planning the implant components such that, after the implants are installed, the limb is in an appropriate or desired alignment (e.g., limb alignment is restored to its pre-disease state and/or the limb will have a postoperative alignment that is neutral or near neutral for the particular patient). In conventional implant planning, a surgeon typically plans implant placement using preoperative images (e.g., CT scans) of the patient's joint. Because the disease state may prevent the limb from achieving the desired pose, however, the preoperative images may not enable the surgeon to accurately assess how the femur and tibia would move relative to one another in the desired alignment. As a result, the surgeon may have difficulty determining how to place and orient each implant component to postoperatively achieve the desired limb alignment throughout the range of motion of the joint.
Additionally, there are different philosophies for addressing the disease state, such as the restoration philosophy and the correction philosophy. The restoration philosophy, which is the prevailing philosophy, is to achieve a postoperative outcome that “restores” the leg alignment to its pre-diseased state. The correction philosophy seeks to attain a postoperative result that “corrects” the leg alignment to a predefined alignment. For example, in the restoration philosophy, the limb is aligned to properly tension the soft tissue (e.g., the ligaments). The alignment at which the soft tissues are properly tensioned is typically close to neutral but may vary for each individual based on anatomical variations. In contrast, under the correction philosophy, the leg is placed in a predefined alignment with the soft tissue being modified (as necessary) to achieve and maintain the predefined alignment. Regardless of the philosophy used by the surgeon, for a patient having disease in the medial compartment of the knee joint, the postoperative restored or corrected alignment will be less varus. Similarly, for a patient having disease in the lateral compartment, the postoperative restored or corrected alignment will be less valgus.
In view of the foregoing, a need exists for surgical methods and devices which can overcome the aforementioned problems so as to enable intraoperative implant planning for accurate placement and implantation of joint implant components, where the implant plan is customized to the patient's unique anatomy and postoperatively achieves a desired limb alignment concurrent with appropriate ligament tension throughout the range of motion of the joint.